Minimal Clinically Important Difference for the Jamar Hand Grip Dynamometer in CIDP: A Korea-UK Study

Grip strength (GS) is widely used in chronic inflammatory demyelinating polyradiculoneuropathy (CIDP). Current guidelines recommend a 10% relative change as the minimal clinically important difference (MCID) to determine response to treatment, preferably based on the average of three consecutive daily measurements. However, appropriate thresholds remain unclear for identifying deterioration and for situations where daily monitoring is not feasible.

We analyzed 350 GS assessments from 122 CIDP patients across 2 neuromuscular centers in Korea and the UK. Clinical changes were classified as improved, deteriorated, or stable based on the patient's perception of change and validated outcome measures: Inflammatory Neuropathy Cause and Treatment (Korea), Overall Neuropathy Limitation Scale (UK), and Inflammatory Rasch-built Overall Disability Scale (both sites). The Youden index was used to determine optimal MCID thresholds for absolute (kg) and relative (%) changes for improvement and deterioration, respectively. The performance of derived cut-offs was compared with previously proposed thresholds.

The guideline-recommended 10% relative threshold showed notably low specificity and accuracy despite high sensitivity for both improvement and deterioration. Our derived thresholds, 5 kg for improvement, 4.5 kg for deterioration, and 20% for either direction of change, offered significantly higher specificity and accuracy.

Our findings highlight the need for more stringent thresholds than current recommendations when assessing patients based on single-day measurements. Our proposed thresholds, double in amplitude of the currently guideline-recommended relative value but close to that previously derived for the absolute cut-off, offer improved diagnostic specificity, which may ensure more reliable monitoring in routine care.